Parallax principle has been discovered more than 100 years. Although naked eye 3D display prototype is demonstrated by domestic and foreign enterprises, the naked eye 3D display device based on the parallax principle has not really entered the field of consumer electronics due to a low image resolution and easily generated visual fatigue. The parallax principle includes a parallax barrier method, a microcolumn lens method and a directional backlight method. A parallax barrier screen or a microcolumn lens plate covers a surface of a liquid crystal display (LCD), so as to achieve angle separation for images with different perspective in space. Based on the optics theory, the image is not unique in different space perspectives due to light source diffusion. Therefore, it is easy to cause visual fatigue when the human eye observes the 3D image.
In Chinese Patent Application CN20101058659.4, 2D/3D switching through a flexible slit grating is provided, but the display effect is greatly affected by the viewing position. In Chinese Patent Application CN201320143064.8, a 3D directional backlight imaging system is provided, which uses two projection lenses and a directional 3D optical structure to realize the naked eye 3D display. In Patent Application US20050264717A1, a 3D display device with a liquid crystal display and a directional backlight module is disclosed, which instantly switches on and off a left and a right backlight source, focuses, into a specific perspective range, the light transmitted through a light guide plate, and forms a 3D image through an alternating projection. With this directional backlight technique, only one person can observe although the image resolution is high. In Chinese Patent Application CN201410187534. X, a naked eye 3D backlight module is provided, which uses one or more sets of LED light sources in timing sequence, a convex lens, a polygon prism, and a parallax barrier, and achieves multi-perspective 3D display. However, backlight structure design and precision machining accuracy are difficult to achieve technically, and light crosstalk occurs easily. Thus, there are no actual samples or products of the naked eye 3D display device based on the proposed directional backlight method.
Dot matrix holography can provide a large perspective and reduce the amount of information, but the production of dot matrix grating pixels has been limited by the technique. In Chinese Patent Application CN201310166341.1, a printing method and system for a three-dimensional image is disclosed, in which a continuously changeable space frequency mechanism directly prints a static colorful stereoscopic image based on nano-grating pixels. The combination of the directional backlight display technique and the directional lighting technique to achieve 3D display, is a new technology arising recently. However, it is difficult to design and manufacture the directional backlight, and the manufacturing cost is high.
A hologram is an image carrying amplitude and phase information, which can truly reproduce three-dimensional information without generating visual fatigue. The three-dimensional effect is unrelated to a distance from an observer. The principle of holographic display may be summarized as follows: a three-dimensional virtual image or a three-dimensional real image can be reproduced in the space by the hologram, each point on the hologram transmits information in all directions of the space, and the entire image can be seen at each observation point in the space. In other words, the image information propagates through a light field and converges to the observation point. Therefore, at different observation points in the space, the entire image can be seen at different perspectives without interfering with each other. However, due to limitation in recording materials, amount of information and technical process of hologram, the industrial application of the holographic display has not been achieved for decades.
A dynamic colorful 3D display may be realized by a holographic waveguide backlight structure, which has a large perspective and is suitable for mobile display. In Chinese Patent Application CN201410852242.3, a solution for realizing a dynamic three-dimensional display using a multi-layer directional light guide structure which is made of nano pixel gratings. In Patent Application US20140300960A1, a directional backlight structure is provided, which modulates a distribution of an emergent light field using a pixelated grating, and couples the light of R, G, B through a hexagonal or triangular waveguide structure, so as to realize a directional modulation of a color light. In Patent Application US20140293759A1, a multi-perspective 3D wrist watch structure is provided, which modulates a light field using a pixelated grating structure, and refreshes an LCD image, so that a 3D display is achieved. Similarly, the hexagonal or triangular waveguide structure couples the light of R, G, B to achieve a colorful display. However, in the above patent applications, the hexagonal or triangular waveguide structure is adopted, which is difficult to be applied to a current mainstream display mode, especially is difficult to be applied to a rectangular display of smart phones, thus is disadvantageous for a large-scale industrial production.
In Patent Application WO2014/051624 A1 of Hewlett-Packard Company, a directional backlight integrated with hybrid laser waveguide arrays is disclosed, so as to achieve a multi-perspective display. The waveguide array is adopted to couple the light of red, green and blue, and the light is exported directionally through a pixelated grating. Although a colorful 3D display can be achieved with this method, the image resolution is greatly reduced due to a multi-waveguide array, and the accuracy requirement for the manufacturing process of the directional backlight structure is high.
The laser display is to perform scanning on the screen using light-spots of the red, green, blue, so as to form an image. With a wide color gamut, a high brightness, and a large breadth, the laser display is an important way to achieve a large size display in the future. However, there is no laser-based naked eye 3D display solution at present. Therefore, a naked eye 3D display device which has no visual fatigue, and has a wide color gamut, a high brightness and a large breadth is urgently needed in the industry.